The acceptance of extracorporeal oxygenation devices based on gas transfer through a membrane will depend to a large extent on the availability of easier to use, safer and less costly devices. Oxygenators using microporous hollow-fibers have come into wider use the last five years. They present more membrane surface to blood and gas phases for equivalent volume (i.e. lower priming volume) and do not require a supplemental secondary flow for adequate gas transfer. These devices do however, suffer from problems associated with all membrane oxygenators made from microporous materials - possible blood damage due to microbubble intrusion, excessive water transport and seepage (flooding) and a lack of selectivity in exchanging gases (oxygen and carbon dioxide). This proposal suggests an improvement to the present state-of-the-art microporous based hollow fiber oxygenators that eliminates all the problems listed above. We propose to develop a composite permselective/microporous hollow fiver device of optimum geometry and membrane characteristics. The optimized hollow fiber geometry will be combined with PAS materials which have been shown to have superior permeability to carbon dioxide and oxygen and high bio-compatibility with blood. IN Phase I techniques were successfully developed for coating the lumen of hollow fibers with a thin coating of a highly permeable polymer (BIOBLAND). Phase II will pursue the continual development and testing of a multifiber coated device and use comparison with uncoated devices.